UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS. 


COLLEGE  OF  AGRICULTURE. 


AGRICULTURAL  EXPERIMENT  STATION. 


SPRAYING  WITH  DISTILLATES. 


By  W.  H.  VOLCK. 


LEAF  SPOTTED  WITH  DISTILLATE. 


BULLETIN  No.    153. 

(Berkeley,  June,  1903.) 


W.  W.  SHANNON, 


SACRAMENTO : 

SUPERINTENDENT  STATE  PRINTING. 
1903. 


BENJAMIN  IDE  WHEELER,  Ph.D.,  LL.D.,  President  of  the  University. 

EXPERIMENT  STATION  STAFF. 

E.  W.  HILGARD,  Ph.D.,  LL.D.,  Director  and  Chemist. 

E.  J.  WICKSON,  M.A.,  Horticulturist,  and  Superintendent  of  Central  Station  Grounds. 

W.  A.  SETCHELL,  Ph.D.,  Botanist. 

ELWOOD  MEAD,  M.S.,  C.E.,  Irrigation  Engineer. 

R.  H.  LOUGHRIDGE,  Ph.D.,  Agricultural  Geologist  and  Soil  Physicist.    (Soils  and  Alkali. 

C.  W.  WOODWORTH,  M.S.,  Entomologist. 

M.  E.  JAFFA,  M.S.,  Assistant  Chemist.    (Foods,  Fertilizers.) 

G.  W.  SHAW,  M.A.,  Ph.D..  Assistant  Chemist.    (Soils,  Beet-Sugar.) 

GEORGE  E.  COLBY,  M.S.,  Assistant  Chemist.    (Fruits,  Waters,  Insecticides.) 

RALPH  E.  SMITH,  B.S.,  Plant  Pathologist. 

A.  R.  WARD,  B.S.A.,  D.V.M.,  Veterinarian,  Bacteriologist. 

E.  H.  TWIGHT,  B.Sc,  Diplome  E.A.M.,  Viticultunst. 

E.  W.  MAJOR,  B.Agr.,  Dairy  Husbandry. 

A.  V.  STUBENRAUCH,  M.S.,  Assistant  Horticulturist  and  Superintendent  of  Substations. 

WARREN  T.  CLARKE,  B.S.,  Assistant  Field  Entomologist. 

H.  J.  QUAYLE,  B.S.,  Assistant  Entomologist. 

H.  M.  HALL,  M.S.,  Assistant  Botanist. 

GEORGE  ROBERTS,  M.S.,  Assistant  Chemist  in  Charge  Fertilizer  Control. 

C.  A.  TRIEBEL,  Ph.G.,  Student  Assistant  in  Agricultural  Laboratory. 

C.  A.  COLMORE,  B.S.,  Clerk  to  the  Director. 

EMIL  KELLNER,  Foreman  of  Central  Station  Grounds. 


JOHN  TUOHY,  Patron,  ) 

y  Tulare  Substation,  Tulare. 


y  Coast  Range  Substation,  Paso  Robles. 


JULIUS  FORRER,  Foreman 

R.  C.  RUST,  Patron, 

y  Foothill  Substation,  Jackson. 
JOHN  H.  BARBER,  Foreman, 

S.  D.  MERK,  Patron, 

J.  H.  00 LEY,  Workman  in  charge, 

S.  N.  ANDR0U3,  Patron,  )  (  Pomona. 

_   „         „  y  Southern  California  Substation,   ■{ 

J.  W.  MILLS,  Foreman,      )  (  Ontario. 

V.  C.  RICHARDS,  Patron,         ) 

m   T    T,ATTTmvmT,r.         ^  f  Forestry  Station,  Chico. 

T.  L.  BOHLENDER,  %n  charge,  ) 

ROY  JONES,  Patron 

_    _  }•  Forestry  Station,  Santa  Monica. 

WM.  SHUTT,  Foreman   ' 


The  Station  publications  (Reports  and  Bulletins),  so  long  as  available, 
will  be  sent  to  any  citizen  of  the  State  on  application. 


CONTENTS. 


Page. 

INTRODUCTORY  NOTE;  by  C.  W.  Woodworth.... 5 

DISTILLATES,  THEIR  COMPOSITION  AND  USE _ 5 

Composition _ . 6 

Analyses,  by  G.  E.  Colby..- 7 

Method  of  use _ 8 

Emulsions _ - 8 

Mechanical  mixtures  .._ . _ 9 

OILS  AS  INSECTICIDES 10 

PENETRATION  OF  OILS  INTO  THE  PLANT 11 

Leaf  structure _ 11 

Diffusion  of  oil  in  leaves _.  12 

Condition  of  the  plant 13 

CONDITIONS  AFFECTING  THE  AMOUNT  OF  INJURY  TO  PLANTS 14 

Quantity  ofoil... _.  14 

Character  of  the  oils 15 

Effects  of  mixed  oils _. _ 16 

General  and  local  injury 16 

METHODS  OF  APPLICATION  OF  OILS 17 

Overshot  and  undershot 17 

Duration  of  application _. 18 

Influence  of  weather  conditions 19 

NATURE  OF  INJURY  PRODUCED  BY  OILS..  19 

Physical  injuries;  Internal  insulation  ;  Rapid  injuries 19 

Chemical  injuries  by  oils 22 

RESISTANCE  OF  THE  PLANT  TO  INJURY  BY  OILS 23 

Variegated  leaves;  Effect  of  temperature _ 24 

PRACTICAL  SUGGESTIONS  FOR  THE  USE  OF  OILS 25 

Black  scale 25 

Red  spider _ 26 

Injury  to  plant 26 

Spotting  and  dropping  of  fruit;  Two  sprayings  annually 26 

PREVENTION  OF  INJURY  FROM  SPRAYING ._ 28 

Overshot  spraying _ _ 28 

Combined  spraying _ _ 29 

Oil  to  be  used 30 


SPRAYING  WITH  DISTILLATES. 


Introductory  Note.— The  "  spotting  "  of  oranges  results  in  considerable  losses  to  grow- 
ers of  this  fruit,  and  many  causes  have  been  assigned  as  producing  it.  Some  of  these 
alleged  causes  certainly  have  no  relation  to  the  trouble  at  all.  Spots  can  be  produced 
by  mechanical  injury,  or  by  chemicals  used  to  kill  insects.  Commonly  one  can  readily 
distinguish  between  the  spots  due  to  either  friction,  fumigation,  or  distillate  spraying; 
and  can  also  distinguish  these  from  spots  caused  in  other  ways.  Growers  usually  fail 
to  realize  the  possibility  of  a  variety  of  causes,  and  assign  the  whole  difficulty  to  one  or 
another  of  the  real  or  supposed  sources  of  the  trouble. 

Spraying  with  distillates  has  probably  caused  more  loss  by  spotting  than  any  other 
one  thing. 

The  study  of  this  subject  was  first  undertaken  by  this  Station  some  two  years  ago. 
Further  studies  and  observations  of  the  results  of  field  operations  were  made  last  sum- 
mer, and  finally  in  connection  with  the  study  of  the  red  spider  of  citrus  trees,  reported 
in  Bulletin  No.  145,  Mr.  Volck  was  able  to  bring  out  of  the  work  the  conclusions  pre- 
sented in  the  following  pages.  This  Bulletin,  therefore,  may  be  considered  as  in  part 
representing  further  results  of  the  cooperation  between  the  Los  Angeles  County  Board 
of  Horticultural  Commissioners  and  the  Entomological  Department  of  the  Experiment 
Station  of  the  University  of  California.  Mr.  Volck  has  opened  the  way  to  a  much 
clearer  appreciation  of  the  problems  of  distillate  spraying  than  has  heretofore  existed. 

C.  W.  WOODWORTH. 

In  sections  where  the  refined  distillation  products  derived  from  crude 
petroleum  are  used  as  insecticides,  it  is  common  to  speak  of  spraying 
with  "distillate"  as  though  referring  to  a  single  definite  substance.  But 
such  a  wide  range  of  oils  and  preparations  of  oils  are  used,  that  this  may 
be  very  misleading;  since  an  opinion  based  upon  the  results  of  any  one 
of  them  would  not  by  any  means  apply  to  all.  It  would  be  less  con- 
fusing, therefore,  to  speak  of  these  products  in  the  plural  sense  as 
distillates. 

The  term  "distillates,"  when  applied  to  petroleum  products,  refers  to 
any  oils  derived  from  crude  oil  by  distillation.  Crude  oils  are  obtained 
from  wells  tapping  natural  reservoirs  of  petroleum  in  the  rocks.  The 
oils  obtained  from  different  wells  may  vary  in  a  marked  degree  in  their 
composition,  but  most  Western  oils  differ  from  the  Eastern  petroleum, 
and  resemble  each  other  to  the  extent  that  they  contain  asphaltum 
instead  of  paraffin  as  their  solid  base.  If  any  of  these  oils  are  placed 
in  a  retort  and  distilled,  the  distillates  will  be  driven  off  in  the  form  of 
vapor,  which  condenses  into  oil  on  cooling.  This  first  distillation 
retains  considerable  asphaltum  and  has  a  dark  color.  It  is  known  as 
"green"  or  raw  distillate.     If  the  green  distillate  is  now  redistilled  and 


6  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT   STATION. 

the  oil  condensed  while  the  retort  is  heating  to  successively  higher 
temperatures,  a  set  of  oils  can  be  successively  collected  corresponding  to 
their  different  boiling  points. 

These  oils  correspond  to  definite  chemical  compounds  with  suc- 
cessively larger  amounts  of  carbon,  but  are  not  sharply  defined;  since 
a  heavier  oil  will  begin  to  pass  over  before  all  the  lighter  oil  has 
evaporated.  In  most  refined  products  there  is  more  or  less  a  mixture  of 
light  and  heavy  oils.  These  oils  belong  to  the  benzine  series;  but  each 
thus  contains  other  oils  of  the  same  series  and  is  charged  with  greater 
or  less  quantities  of  other  substances  occurring  as  impurities.  To 
remove  these  substances  the  oils  may  be  treated  with  sulfuric  acid, 
then  with  caustic  soda,  and  finally  filtered  through  sawdust  to  remove 
water  and  water-soluble  materials,  after  which  they  are  called  "treated 
distillates." 

The  naphtha  and  kerosene  obtained  by  distillation  of  Western  oils  are 
not  often  used  as  spraying  materials,  although  kerosene  might  be  used 
advantageously  in  some  cases.  Likewise  the  heavy  lubricating  oils 
are  not  regarded  as  suitable  for  spraying.  The  distillates  most  used 
are  those  approximating  28°  gravity  (28°  Baume),  and  there  is  some 
disposition  to  use  as  low  as  26°  gravity.  These  oils  lie  between  the 
kerosenes  and  the  lubricating  oils,  and  have  some  of  the  properties  of 
each.  They  dry  more  slowly  than  kerosene,  have  a  characteristic  odor, 
and  when  clarified  range  from  nearly  white  to  a  deep  yellowish-brown 
color. 

The  accompanying  table  of  analyses,  made  by  Mr.  Colby  of  this  Sta- 
tion, shows  the  composition  of  some  of  these  distillates. 

There  are  two  ways  in  which  28°  distillate  may  be  prepared:  first,  by 
mixing  oils  of  higher  and  lower  gravity;  and  second,  by  direct  distilla- 
tion— the  so-called  short-cut  method. 

The  short-cut  distillate  resembles  the  mixed  oils  in  containing  oils  of 
both  higher  and  lower  gravities,  but  there  is  less  range;  by  far  the 
greater  part  of  the  oil  corresponds  closely  to  the  gravity  indicated,  and 
in  the  case  of  28°  gravity  may  be  considered  a  nearly  pure  "gas  distil- 
late." The  short-cut  process  for  the  production  of  spraying  distillates 
is  used  much  more  now  than  formerly. 


SPRAYING   WITH   DISTILLATES. 


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8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

Method  of  Use. — The  most  practical  way  to  use  oils  as  insecticides  is 
to  dilute  them  with  water.  This  is  rather  a  difficult  matter  to  accom- 
plish, since  oil  will  not  dissolve  in  water.  Various  methods  have  been 
devised  to  accomplish  the  mixing  of  water  and  oil.  These  may  be 
divided  into  two  classes,  the  emulsions  and  the  mechanical  mixtures. 

Emulsions. — The  mechanical  mixing  idea  antedated  the  emulsions, 
but  as  first  handled  it  was  unsatisfactory,  owing  to  the  imperfect 
nature  of  the  machinery  used.  In  order  to  overcome  the  disadvantages 
of  the  mechanical  process  two  forms  of  soap  emulsions  were  devised, 
one  by  Professor  A.  J.  Cook,  and  another  by  Professor  C.  V.  Riley  and 
his  assistant,  Mr.  Hubbard.  Eastern  kerosene  was  employed,  and  for  a 
long  time  this  was  the  only  oil  used  in  spraying. 

Kerosene  emulsions,  when  prepared  with  care,  are  stable  and  very 
satisfactory  as  spraying  materials;  they  have  had  wide  application  in 
the  East,  and  to  a  less  extent  also  on  this  Coast.  The  relatively  high 
cost  of  this  oil  limits  its  availability  as  an  insecticide. 

In  recent  years,  with  a  view  of  obtaining  a  cheaper  insecticide,  many 
other  oils  have  been  tried,  notably  California  distillates;  but  it  was  at 
once  observed  that  the  light  kerosenes  prepared  from  these  Western  oils 
did  not  emulsify  well,  and  when  used  on  the  trunk  of  the  tree  in  large 
quantities  for  scale  insects,  the  separated  oil  often  accumulated  at  the 
surface  of  the  ground  and  resulted  injuriously.  This  difficulty  was 
partly  overcome  by  using  heavier  oils,  and  gas  distillate  of  28°  Baume 
became  quite  generally  adopted. 

The  emulsions  made  from  California  oils  have  not  usually  been  as 
satisfactory  as  those  from  Eastern  kerosene,  and  a  large  amount  of  dam- 
age has  been  done  by  separated  oil,  which  rises  to  the  surface  in  the 
spraying  tanks.  The  desire  of  the  sprayers  to  be  economical  of  material 
causes  them,  when  the  tank  gets  low,  to  finally  spray  this  separated  oil 
onto  the  trees. 

Permanent  emulsions  are  prepared  by  breaking  the  oil  up  into  fine 
particles  in  a  fluid  which  has  sufficient  surface  tension  to  prevent  them 
from  readily  uniting  together.  The  small  size  of  the  droplets  decreases 
the  natural  tendency  of  the  oil  to  rise  to  the  surface.  When  milk  is 
used  as  an  emulsifier  a  compound  emulsion  is  produced,  the  casein 
particles  coating  the  oil  globules. 

Soap  is  the  cheapest,  and  therefore  ordinarily  the  best  emulsifying 
material.  Soaps  differ  much  in  their  emulsifying  properties.  Whale- 
oil  soap  usually  gives  very  satisfactory  results,  as  do  also  certain 
vegetable  soaps.  In  place  of  these,  common  laundry  soap,  which  is 
cheaper,  may  be  used.     The  standard  formula  for  kerosene  emulsion  is: 

Riley.  Cook. 

Soap 14  pound  %  pound 

Water 1  gallon  1  gallon 

Oil - - 2  gallons  1  quart 

Dilute  with  water,  after  emulsifying,  to 30  gallons  4  gallons 


SPRAYING    WITH    DISTILLATES.  9 

With  28°  or  26°  distillates  a  pound  of  soap  (dissolved  in  a  gallon  of 
water)  to  a  gallon  of  oil  gives  good  results.  In  preparing  the  emulsion 
the  soap  is  dissolved  in  the  water  by  boiling,  and  the  oil  is  added  while 
this  spray  solution  is  hot;  the  whole  being  churned  very  vigorously 
until  the  emulsion  is  formed. 

Other  emulsifying  materials  have  been  used,  such  as  sour  milk,  and 
the  juice  of  such  plants  as  the  soap  plant  (Chlorogalum). 

But  the  preparation  of  stable  emulsions  is  a  difficult  matter  and  it 
will  not  be  necessary  to  go  deeply  into  the  subject  in  this  bulletin,  as 
they  have  largely  been  superseded  by  mechanical  mixing  methods. 

The  emulsions  have  proved  unsatisfactory,  primarily  because  of  the 
difficulty  of  obtaining  a  stable  article.  If  the  oil  separates  and  rises 
to  the  surface  and  is  then  pumped  on  the  foliage  in  a  pure  state,  great 
injury  may  result;  in  fact,  the  largest  part  of  the  serious  injury  to  trees 
credited  to  distillate  sprays  may  be  traced  to  the  bad  effects  of  the 
separated  oil. 

Mechanical  Mixtures. — While  the  mechanical  mixing  idea  preceded 
the  emulsions,  it  is  only  in  recent  years  that  it  has  been  perfected  and 
made  practicable.  There  are  several  types  of  machinery  which  may  be 
used  to  form  mechanical  emulsions,  but  they  all  operate  to  break  up  the 
oil  into  fine  particles  and  keep  it  suspended  in  water  by  some  kind  of 
agitation.  All  such  methods  require  the  constant  use  of  power  to  keep 
the  oil  and  water  mixed.  In  several  spray  outfits  the  entire  body  of 
the  oil  and  water  carried  into  the  field  is  rotated  or  churned  by  means 
of  a  paddle  working  at  such  a  speed  that  the  oil  is  mixed  with  the  water 
and  broken  up  into  such  small  particles  that  the  mixture  looks  milky. 
This  mechanical  emulsion  is  then  pumped  through  the  nozzles  and 
applied  as  a  spray. 

In  other  machines  the  oil  and  water  are  carried  in  separate  tanks  and 
mixed  in  the  process  of  pumping.  The  oil  and  water  may  be  drawn 
into  a  single  pump  and  the  proportions  regulated  by  valves;  or  separate 
pumps  of  different  sizes  may  be  used.  With  this  system  a  baffling 
chamber  or  cylinder  is  sometimes  used.  In  the  baffling  chamber 
obstructions  are  placed,  so  that  when  the  mixture  is  passed  through  it 
there  is  considerable  friction,  which  is  intended  to  bring  about  a  more 
perfect  emulsion. 

Mechanical  mixing  represents  the  most  modern  idea  in  practical 
spraying,  and  is  certainly  a  great  improvement  over  the  "stable"  emul- 
sions, which  were  so  only  in  name. 

In  the  case  of  citrus  fruits  there  is  another  reason  why  the  mechanical 
mixtures  are  superior  to  stable  emulsions.  The  spotting  of  the  fruit, 
which  is  due  to  the  accumulation  of  oil  by  the  drying  of  the  large  drops 
which  form  on  the  under  side  of  the  orange,  is  noticeably  greater  with 
these  emulsions. 


10  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

The  oil  in  the  latter  is  practically  all  held  in  the  drop  until  the 
water  evaporates,  when  the  emulsion  breaks  down  and  the  distillate 
penetrates  the  rind.  In  the  mechanically  mixed  drop,  however,  the  oil 
separates  more  quickly  and  seems  to  spread  out  over  a  relatively  greater 
surface,  and  for  this  reason  may  not  do  much  damage. 

OILS   AS   INSECTICIDES. 

The  distillates  are  not  the  only  oils  having  insecticidal  properties;  in 
fact,  nearly  all  oils  are  capable  of  killing  insects;  but  it  is  the  volatile 
oils  that  are  most  effective,  their  vapors  having  far  greater  penetrating 
power  than  the  oils  in  the  liquid  form.  Death  by  suffocation,  due  to 
the  clogging  of  the  breathing  pores  of  the  insect,  is  only  possible  with 
the  heavier  and  more  slowly-drying  oils,  and  death  in  this  manner  even 
with  these  is  only  a  matter  of  conjecture.  Commercial  distillates 
contain  a  wide  range  of  oils  so  brought  together  as  to  make  up  their 
definite  degree  of  gravity.  Some  of  the  heavy  oils  found  in  the  distillate 
may  be  very  slow-drying,  while  the  lighter  parts  will  be  correspond- 
ingly volatile. 

This  mixture  of  oils  is  apparently  more  effective  than  the  pure 
volatile  products,  which  may  be  explained  on  the  ground  that  the  heavy 
oils  prevent  the  too  rapid  dissipation  of  the  volatile  parts.  While  the 
vapor  is  doubtless  the  condition  in  which  oils  exhibit  their  more  evident 
insecticidal  effect,  the  oils  are  certainly  most  effective  when  the  liquid 
comes  in  immediate  contact  with  the  insect.  The  vapor  given  off  by 
oil  which  has  been  sprayed  on  parts  of  the  tree  not  infested  with  insects 
is  usually  too  much,  or  too  diluted  by  the  air,  to  be  effective  on  the  parts 
that  are  infested. 

Insects  capable  of  motions  show  signs  of  great  irritation  and  weakness 
when  brought  into  contact  with  small  particles  of  a  volatile  oil.  But 
if  the  dose  has  not  been  too  large,  recovery  always  takes  place. 

The  black  scale,  which  is  stationary  during  the  greater  part  of  its  life, 
is  not  capable  of  exhibiting  other  symptoms  of  the  effect  of  an  oil  than 
the  loosening  of  the  insect's  grasp  on  the  tree,  so  that  it  will  "slip" 
much  more  easily  than  when  not  affected.  This  loosening  is  noticeable 
a  few  minutes  after  spraying,  and  is  possibly  due  to  two  causes:  the 
weakening  of  the  insect  itself,  causing  the  muscles  of  the  labium  to 
relax,  and  the  softening  of  the  gummy  matter  which  the  insect  secretes 
under  its  body  and  which  helps  to  hold  it  to  the  tree.  With  this  insect 
also,  recovery  may  take  place,  and  insects  which  are  quite  loose  soon 
after  spraying  will  often  regain  their  hold. 

It  is  possible,  by  increasing  the  amount  of  oil  applied,  to  arrive  at  a 
point  where  all  insects  will  be  killed;  but  the  difference  in  the  resistance 
of  the  insects  and  the  plants  infested  by  them  may  not  be  great  enough 
in  some  cases  to  allow  the  use  of  oil  without  danger  to  the  plant. 


SPRAYING    WITH   DISTILLATES.  11 

PENETRATION    OF    OILS    INTO    THE    PLANT. 

By  far  the  greatest  cause  of  injury  to  vegetable  tissues  is  brought 
about  by  the  penetration  of  the  oils  applied,  into  the  interior  of  the  plant. 
Any  one  who  has  examined  carefully  a  plant  which  has  recently  been 
sprayed  with  a  distillate,  especially  one  made  of  the  heavy  oils,  will 
notice  blotch-like  spots  beneath  the  surface  which  are  somewhat  darker 
than  the  surrounding  tissues.  (See  frontispiece.)  These  spots  are 
evidently  due  to  the  presence  of  oil  which  has  penetrated  the  tissue  of 
the  plant,  and  owing  to  its  slight  volatility  this  may  remain  for  weeks 
or  even  months. 

Leaf  Structure. — The  rate  of  the  penetration  of  a  fluid  into  the  leaf 
from  the  surface  largely  depends  on  the  presence  of  appreciable  openings 
through  which  it  may  pass,  and  when  this  fluid  is  in  limited  quantities 
other  factors  enter — such  as  the  surface  tension  of  the  fluid  itself,  and 
the  distribution  of  the  oil  on  the  leaf.  Sometimes  the  surface  of  a  leaf 
is  smooth  and  free  from  hairs,  as  is  seen  in  the  guava  and  orange;  while 
in  other  cases  it  is  covered  with  a  more  or  less  dense  growth  of  hairs,  as 
in  the  morning-glory  and  quince.  If  a  drop  of  oil  is  placed  on  an 
orange  leaf  it  will  not  spread  greatly  over  the  surface,  but  if  the  same 
drop  were  placed  on  a  morning-glory  leaf  the  hairs  would  act  as  a  wick, 
spreading  the  drop  out  over  a  considerable  area.  If  the  morning-glory 
leaves  were  as  resistant  to  oils  as  are  the  orange  leaves  the  injury  would 
be  far  less. 

If  a  drop  of  oil  is  placed  on  the  upper  and  lower  surface  of  an  orange 
leaf  it  will  be  seen  that  the  one  on  the  lower  surface  will  soak  through 
the  epidermis,  while  that  on  the  upper 
surface  will  often  remain  until  it  evapo- 
rates. If  the  epidermis  of  the  leaf  is 
examined  under  the  microscope,  the  upper 
one  will  show  a  comparatively  smooth  and 
unbroken  surface,  while  the  lower  epider- 
mis will  be  found  closely  sprinkled  with 
openings  known  as  stomata.  A  stoma  is 
not  a  simple  opening,  but  is  provided  with 
a  valve-like  arrangement  of  cells  around  it, 
which  expand    and   contract  according  to       fig.  i.  a  fragment  of  the  lower 

the    amount    of    moisture    within    the    leaf    epidermis  of  an  orange  leaf,  show- 

and  the  relative  humidity  of  the  air.     The 

presence  of  these  stomata  easily  explains,  then,  the  greater  penetration 

through  the  lower  epidermis. 

Again,  if  a  drop  of  oil  is  placed  on  an  orange  leaf  and  the  epidermis 
under  it  is  punctured  by  a  needle  or  other  sharp  instrument  the  oil  will 
flow  in  very  rapidly,  showing  that  any  injury  to  the  surface  of  the  leaf 


12  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION. 

may  help  the  oil  to  gain  entrance.  If  this  experiment  is  performed  at 
the  same  time  on  the  upper  and  lower  surfaces  it  will  be  seen  that  as 
the  oil  spreads  beneath  the  epidermis,  forming  regular  patches  with  the 
point  of  entrance  as  a  center,  the  patch  on  the  lower  surface  will  spread 
much  faster  than  that  on  the  upper  one.  The  explanation  of  this  is 
found  in  the  structure  of  the  inside  of  the  leaf.    (Fig.  2.) 

Generally  speaking,  a  section  of  a  leaf  at  right  angles  to  the  upper 
and  lower  surfaces  will  show  the  cells  to  be  arranged  after  the  following 

plan:  The  upper  surface  is  made  up  of  a  row 
of  light-colored  cells — the  epidermis.  These 
are  thin-walled  and  empty  in  the  case  of  the 
leaves  of  citrus  trees.  Beneath  this  is  a  layer 
of  closely  packed,  elongated,  and  somewhat 
pointed  green  cells,  arranged  with  their  points 
toward  the  surface  layer,  or  crosswise,  of  the 
section.  These  are  known  as  the  palisade  cells, 
and  in  combination  form  the  palisade  layer. 
Under  the  palisade  layer  is  a  layer  of  large, 
irregular  cells,  which  are  loosely  joined  to- 
gether, leaving  spaces  and  passages  between 
8tfuc^ofa7o^eU™  them.  These  cells  are  also  green,  but  paler 
cross-section  of  a  vascular  bun-   than  the  palisade  layer.    They  constitute  what 

is  known  as  the  spongy  layer.  The  spongy 
layer  extends  to  the  lower  epidermis  of  the  leaf.  The  tightly  packed 
palisade  layer  on  the  upper  side  gives  little  space  for  the  spread  of  oil, 
but  below  this  the  loose  structure  of  the  spongy  layer  furnishes  just  the 
right  sort  of  passageway  for  the  rapid  spread  of  the  oils. 

Aside  from  the  green  parts  of  the  leaf  there  is  the  framework  of 
vascular  bundles,  constituting  the  ribs  and  veins,  which  in  some  cases, 
notably  the  orange  and  guava  (see  Fig.  2),  are  buried  within  the  layers 
of  green  cells;  while  in  others,  as  the  apricot  (see  Fig.  3),  peach,  and 
morning-glory,  the  vascular  bundles  connect  with  the  epidermis  both 
above  and  below.  The  vascular  bundles  are  woody  and  compact  struc- 
tures, very  different  from  the  rest  of  the  leaf.  In  the  orange  leaf  the 
veins  offer  little  resistance  to  the  flow  of  the  oil;  but  this  is  not  the  case 
with  such  a  leaf  as  that  of  the  morning-glory  or  apricot,  where  the  vas- 
cular bundles  uniting  closely  with  the  epidermis  very  effectively  impede 
the  flow  of  oil  from  one  part  of  the  tissue  to  another. 

Diffusion  of  Oil. — This  structural  difference  in  leaves  is  a  very  impor- 
tant factor  in  the  toxic  effect  of  oils.  Thus,  for  instance,  in  the  orange 
leaf  a  drop  of  oil  entering  at  one  point  may  become  diffused,  spreading 
over  so  large  an  area  that  it  may  volatilize  so  soon  as  to  cause  little 
injury.     On  the  other  hand,  in  an  apricot  leaf,  the  oil  being  restricted 


SPRAYING   WITH   DISTILLATES.  13 

by  the  vascular  net  to  a  small  area,  the  same-sized  drop  will  do  injury 
before  it  can  evaporate.  With  the  apricot  and  morning-glory  the  pene- 
trated parts  are  usually  killed,  the  line  of  killing  being  irregular  and 
following  the  vascular  bundles. 

It  should  be  mentioned  in  this  connection  that  the  structure  of  the 
fruit  rind  of  citrus  fruits  is  in  some  particulars 
much  the  same  as  that  of  the  leaf,  there  being 
stomata  sprinkled  over  the  surface,  with  green  cell 
tissue  beneath.  Distillate  penetrates  the  rind,  and 
if  a  heavy  oil,  it  remains  for  a  long  time,  if  not 
indefinitely,  and  thus  forms  the  much-talked-of 
spotting. 

Returning  to  the  diffusion  of  oil  through  an  unin- 
terrupted spongy  layer,  it  is  evident  that  the  capil- 
larity of  the  oil  must  have  much  to  do  with  the  ^on  oiTywli^^i- 
amount  of  the  spread.  The  viscosity  also,  which  die  of  an  apricot  leaf, 
tends  to  act  against  the  capillarity  by  increasing  the  time  required  for 
a  given  body  of  oil  to  pass  through  a  capillary  opening,  has  its  effect  on 
the  spreading.  This  is  well  illustrated  by  placing  a  drop  of  kerosene 
and  a  drop  of  a  lubricating  oil  upon  the  same  leaf;  the  kerosene  quickly 
diffuses  through  the  cell  structure,  while  the  lubricator  acts  much  more 
slowly  and  never  spreads  as  far.  Thus  the  heavy  oils,  in  addition  to 
their  slow  drying,  aggravate  the  difficulty  by  remaining  locally  concen- 
trated. 

Condition  of  the  Plant. — Aside  from  simple  points  of  structure,  the 
condition  of  the  leaf  greatly  affects  the  behavior  of  oils  toward  it.  The 
flowing  of  oil  through  the  cell  interspaces  is  quite  a  different  thing 
from  the  penetration  of  the  cells  themselves,  or  even  the  complete 
isolation  of  the  individual  cells,  both  of  which  must  occur  to  some 
extent  in  the  penetration  of  oils  beneath  the  epidermis.  Generally 
speaking,  oil  can  not  take  the  place  of  water,  therefore  an  active  cell 
well  filled  with  water  would  be  least  likely  to  suffer  in  this  way.  But 
cells  which  are  partly  dried  out  and  whose  surfaces  have  become  dry 
may  be  penetrated  or  sealed  over  by  the  oil.  Thus  the  mechanical 
effects  of  oils  are  often  sufficient  to  render  parts  of  sprayed  leaves 
functionless.  If  this  isolation  lasts  long,  it  is  alone  sufficient  to  account 
for  a  large  amount  of  the  injury  due  to  distillates.  The  age  and  health 
of  the  plant  and  leaf  largely  determine  the  amount  or  extent  of  the 
conditions  which  affect  penetration.  The  older  a  leaf  becomes,  the 
rougher  the  skin  and  greater  the  probability  of  having  received  injuries. 
But  the  extreme  young  leaves,  on  the  other  hand,  are  more  liable  to  be 
completely  covered  by  a  film  of  oil,  and  so  killed.  The  old  leaves  are 
much  drier  and  therefore  more   penetrable,    and  consequently  suffer 


14  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

most  if  they  receive  the  same  treatment  as  do  the  younger  leaves. 
However,  on  the  tree  such  leaves  are  often  so  protected  by  the  outside 
newer  ones  that  in  practice  they  often  escape.  In  general,  old  leaves 
are  most  affected  and  the  natural  falling  process  much  hastened. 

CONDITIONS   AFFECTING   THE   AMOUNT    OF   INJURY. 

The  greatest  need  for  further  work  with  oils  is  to  determine  their 
effect  on  plants  under  carefully  determined  conditions.  A  beginning 
has  been  made  along  a  number  of  lines,  but  only  that  which  has  clearly 
led  to  definite  conclusions  can  be  now  reported. 

Quantity  of  Oil. — In  order  to  determine  more  accurately  the  effect  of 
oils  on  the  plant,  small  quantities  of  oil  were  measured  off  and  applied 
to  leaves  of  definite  sizes. 

The  branches  chosen  for  the  experiment  were  what  are  knownjas 
water-sprouts.  These  grow  larger  leaves  than  the  fruiting  branches 
and  give  a  greater  number  on  the  same  twig,  which  can  be  utilized  for 
checks  and  experiments. 

The  practice  was  to  begin  with  the  lower  leaves  and  work  toward  the 
tip  of  the  branch,  first  applying  a  definite  amount  of  oil  to  the  under 
side  of  a  leaf,  then  to  the  upper  side  of  the  next  leaf,  and,  lastly,  the 
same  amount  of  oil  was  spread  over  both  surfaces  of  a  similar  leaf. 
This  operation  was  usually  repeated  three  times  on  a  sprout,  and  check 
leaves  were  left  all  along  the  stem.  The  data  of  two  of  these  tests  are 
as  follows: 

TABLE  II.    Experiments  on  Leaves  with  Different  Amounts  of  Oil. 

Eastern  Kerosene.    Applied  November  28th. 

Leaf  Area  of  each  side                Quantity  of  Oil  Used.  Amount  of  Date  of 

No.  of  Leaf  Surface.       Upper  Surface.  Lower  Surface.      Yellowing.  Falling. 

1  68.76  sq.  cm.  ...  .12  cc.                slight              

2  73.84      "  .12  cc.  ...  slight 

3  81.53       "  .06  .06  slight 

4  57.69       "  ...  .12                     slight               

5  58.45       "  .12  ...  slight 

6  56.66       "  .06  .06                      slight 

7  42.92       "  ...  .06 _. 

8  46.66       "  .06  ...                     _ _. 

9  38.35       "  .03  .03                     

Short-cut  28°  Distillate.     Applied  November  19th. 

1  69.23  sq.  cm.  ...  .05  cc.  slight  

2  70.30  "  .05  cc.  ....  _. 

3  70.00  "  .025  .025 Nov.  27 

4  56.61  "  ...  .05  ._ Nov.  27 

5  51.57  "  .05 

6  51.07  "  .025  .025 Nov.  28 

7  47.76  "  ...  .05  Nov.  28 

8  42.79  "  .05  ... _. 

9  39.69  "  .025  .025  noticeable 


SPRAYING   WITH   DISTILLATES.  15 

These  experiments  were  repeated  a  number  of  times  with  various  oils 
and  dilutions,  and  brought  out  the  following  results: 

First — The  upper  surfaces  of  the  leaves  were  always  able  to  resist 
amounts  of  oil  which  proved  fatal  when  applied  to  the  lower  surface  of 
corresponding  leaves;  but  the  oil  applied  to  the  upper  surface  had  some 
effect,  and  often  caused  a  slight  yellowing  of  the  leaves. 

Second — When  the  same  amount  of  oil  as  was  used  on  a  single  surface 
was  spread  over  both  surfaces  of  a  similar  leaf  it  often  caused  the  falling 
of  the  leaf. 

Third — When  the  whole  amount  of  oil  was  placed  on  the  under  side 
of  the  leaves,  the  result  was  about  the  same  as  when  the  oil  was  placed 
on  both  surfaces,  causing  falling  and  yellowing  where  similar  amounts 
applied  to  the  upper  surface  only  were  but  slightly  injurious. 

It  was  often  noticed  that  the  large  leaves  near  the  base  of  the  water- 
sprout  showed  serious  effects  from  amounts  of  oil  which  the  smaller  and 
younger  leaves  at  the  tip  resisted.  This  can  be  explained  by  the  fact 
that  these  older  leaves  absorbed  the  oil  much  more  readily,  owing  to 
their  drier  and  rougher  epidermis,  while  the  young  leaves  were  quite 
resistant  to  penetration  and  better  supplied  with  water. 

Character  of  the  Oils. — Experiments  were  made  to  ascertain  the  effects 
of  oil  of  different  gravities.  The  oils  were  diluted  to  definite  per  cents 
with  water  in  a  bottle  and  shaken  up  until  well  mixed,  when  the 
mechanical  emulsions,  before  they  had  time  to  separate,  were  poured 
over  small  branches.  It  was  found  that,  among  the  oils  tried  under 
these  conditions,  the  Eastern  kerosene  was  the  least  injurious  to  the 
foliage,  and  that  the  amount  of  injury  for  a  given  per  cent  increased 
very  rapidly  with  the  gravity  of  the  oil.  Kerosene  was  found  to  produce 
no  apparent  injury  on  orange  at  10  per  cent,  while  the  heavier  oils  were 
not  free  from  injury  at  2  per  cent.  It  was  also  shown  that  orange  foliage 
is  much  more  resistant  than  that  of  the  apricot. 

The  above  experiments  also  illustrated,  in  a  very  interesting  manner, 
the  effect  of  oils  of  different  gravity.  The  two  records  will  serve  to  show 
the  comparative  effect  of  a  28°  gravity  distillate  and  Eastern  kerosene. 
By  comparing  the  preceding  table  it  will  be  seen  that  for  leaves  of  the 
same  area  and  age  an  amount  of  kerosene,  which  was  as  large  as  the 
leaves  could  retain  on  their  surfaces,  was  far  less  injurious  than  the 
much  smaller  amounts  of  28°  gravity  distillate.  This  heavy  oil  was 
manufactured  by  the  short-cut  process  and  said  to  be  especially  pure. 

The  spray  distillates  prepared  by  several  refining  companies  were 
tried  in  the  same  way  and  showed  similar  results.  There  has  been 
much  contention  in  favor  of  clarified  oils  for  spraying,  but  in  our  experi- 
ments little  difference  was  found  in  them,  except  that  the  vapor  of 
certain  unclarified  distillates  proved  more  injurious  to  orange  foliage 
than  that  from  the  best  grade  of  short-cut  clarified  oils.     This,  as  shown 


16  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION. 

by  direct  experiments,  is  not  due  to  any  asphaltum  or  nitrogenous 
materials,  but  to  benzines  and  volatile  oils  contained  in  the  less  pure 
products. 

In  our  experience  the  injuries  resulting  from  distillates  are  not  due 
to  any  impurities  contained  in  the  oils,  but  to  the  oils  themselves,  and 
the  only  way  to  diminish  these  injuries  is  to  choose  less  injurious  oils, 
which  evidently  lie  toward  the  kerosenes.  Pure  Eastern  kerosene  has 
given  the  best  results,  but  certain  cheap  Western  kerosenes  have  proved 
quite  satisfactory.  These  can  be  obtained  at  nearly  the  same  price  as 
the  clarified  28°  gravity  oils,  so  the  only  increase  in  the  expense  that 
would  result  would  be  the  greater  amounts  of  these  oils  required  to  be 
effective. 

The  Effects  of  Mixed  Oils. — Some  sprayers  add  turpentine  and  other 
light  oils  to  the  heavy  distillates  to  enhance  their  insecticidal  properties. 
The  effects  of  the  mixed  oils  on  the  plant  are  in  general  very  nearly 
the  average  of  the  effects  produced  by  these  oils  used  independently, 
though  the  addition  of  10  per  cent  turpentine  to  the  28°  B.  oil  used  does 
not  materially  change  the  result.  Turpentine  when  used  alone  produces 
marked  local  injury  and  quick  killing  of  affected  parts,  but  has  slight 
chronic  effect,  owing  to  its  rapid  evaporation.  When  mixed  with  the 
heavy  oils,  turpentine  does  not  show  these  local  effects  in  dilutions  of 
10  per  cent  or  less. 

If  kerosene  and  the  heavy  oils  are  mixed,  the  moderating  effect  of  the 
former  is  soon  noticed.  This  is  well  shown  by  the  following  experi- 
ment; but  as  the  branches  experimented  with  had  to  be  taken  on 
different  trees,  the  results  are  not  in  perfect  ratio  to  the  per  cent  indi- 
cated: Mixtures  of  kerosene  and  Southern  Refining  Company's  28°  B. 
(short-cut)  distillate,  varying  from  1  to  100  per  cent,  were  applied  to 
thirty-three  branches  of  Valencia  orange  trees  on  the  22d  of  November, 
1902.  The  branches  were  chosen  in  nearly  the  same  position  on  the 
trees,  and  all  were  in  about  the  same  condition  of  fruit  and  foliage. 
The  dilution  was  4  per  cent.  On  the  26th  of  December,  1902,  the 
branches  were  all  removed  and  arranged  in  the  order  of  the  apparent 
injury  resulting. 

Beginning  with  the  most  normal  samples  the  per  cents  of  kerosene 
in  the  mixture  read  100,  90,  80,  70,  60,  30,  32,  34,  26,  28,  50,  24,  19,  18, 
20,  19,  16,  15,  17,  10,  12,  11,  13,  14,  9,  1,  6,  5,  8,  7,  3,  4,  2. 

The  effects  of  the  applications  varied  from  almost  nothing  with  pure 
kerosene  to  serious  defoliation  and  loss  of  color  with  the  lower  per  cents, 
showing  clearly  the  injurious  effects  of  the  heavy  oils. 

General  and  Local  Injury. — Along  with  the  quantitative  work  a  series 
of  experiments  were  made  to  determine  the  parts  of  the  plant  where  oils 


SPRAYING    WITH    DISTILLATES. 


17 


can  do  the  greatest  injury.  With  the  citrus  tree,  leaves  often  break  off 
at  the  junction  of  petiole  and  blade  without  showing  any  other  signs  of 
injury.  It  would  seem  from  this  that  the  injury  was  done  at  or  near 
this  point;  but  that  this  is  not  the  case  was  shown  by  many  experi- 
ments. 

In  one  set  of  experiments  oils  and  vaselines  were  applied  to  the 
petiole  and  blade  at  and  near  the  point  of  juncture,  but  falling  did  not 
take  place,  although  the  doses  used  were  often  strong  enough  to  kill  the 
soft  green  pulp. 

In  a  second  set  of  experiments  large  areas  at  the  base  of  the  leaves 
were  treated  successively  with  oils,  both  upper  and  lower  surfaces,  and 
lower  surface  alone.  In  these  experiments,  while  the  parts  covered  with 
oil  soon  became  yellow,  the  leaves  did  not  fall  unless  the  area  covered 
was  at  least  half  of  that  of  the  whole  leaf;  but  the  same  effect  was 
obtained  by  coating  the  outer  half  of  the  leaf. 

These  experiments  were  repeated  often  enough  to  give  perfectly  defi- 
nite demonstration,  and  they  show  that 
the  most  important  injuries  caused  by 
oils  are  general  and  not  local. 

In  the  same  way  oils  were  applied 
to  twigs  and  petioles,  without  coat- 
ing the  leaves.  Here  the  leaves  re- 
mained sound,  but  fermentations  were 
set  up  in  the  stem  which  caused  the 
production  of  gum;  and  very  marked 
gum  disease  can,  therefore,  be  produced 
by  oiling  the  stems  with  a  slow-drying 
oil  like  vaseline. 

METHODS    OF   APPLICATION. 

The  different  methods  of  applying  oils 
and  the  results  are  illustrated  in  the 
accompanying  figures  (Fig.  4). 

From  the  small  experiments  men- 
tioned above,  it  was  seen  that  the  upper 
side  of  a  leaf  is  several  times  more  resist- 
ant to  oils  than  the  lower  surface;  some 
experiments  were  therefore  conducted 
with  a  view  of  applying  this  principle 
in  spraying. 


Occasional  Jallino 


Almost  invariable  fa 


Fig.  4.    The  shading  indicates  portions 
covered  with  oil. 


Overshot  and  Undershot  Spraying. — It  may  prove  convenient  to  use  the 
term  " overshot"  for  downward  spraying,  and  "undershot"  for  spraying 


18  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

upward.  If  emulsions  or  mechanically  mixed  oils  are  sprayed  on  the 
tree,  always  directing  the  nozzle  downward,  the  upper  surfaces  of  the 
leaves  will  be  wet  together  with  considerable  more  than  half  the  surface 
of  the  branches,  for  the  applied  liquid  runs  around  the  twigs  and 
branches,  often  completely  wetting  them. 

Large  branches  of  orange  and  grape-fruit  were  sprayed  as  described 
above  with  various  28°  gravity  distillates,  a  dilution  of  4.5  per  cent 
being  used.  Other  similar  branches  were  sprayed  with  the  same  dilu- 
tion from  beneath,  throwing  the  spray  only  on  the  under  side  of  the 
leaves.  Still  others  were  sprayed  in  the  ordinary  manner;  that  is,  both 
from  above  and  beneath. 

These  experiments  were  repeated  a  number  of  times  with  similar 
results,  as  follows:  In  all  overshot  work  the  foliage  was  very  little 
injured,  and  in  all  undershot  and  normal  spraying  the  injury  was  very 
serious. 

All  the  branches  sprayed  were  well  infested  with  black  scale,  and  it 
was  found  that  the  overshot  method  killed  quite  as  many  as  would  be 
killed  by  normal  spraying  with  1.5  to  2  per  cent  doses,  which  are  as 
great  as  the  tree  can  stand. 

The  effect  of  overshot  spraying  on  the  fruit  is  not  as  promising  as 
that  on  the  foliage,  as  the  large  drops  which  run  down  from  the  upper 
surface  are  liable  to  spot  the  rind.  This  difficulty  may  be  greatly 
obviated  in  practice  by  the  methods  described  in  the  chapter  on  Practical 
Suggestions,  on  page  25. 

The  duration  of  application  is  all-important  with  the  oils.  This  is 
due  to  the  method  of  diluting  with  water  a  body  insoluble  in  the  latter, 
which,  as  has  already  been  stated,  consists  in  breaking  up  the  oils  into 
fine  particles  held  apart  by  the  water  of  dilution.  As  oils  are  sticky  or 
adhesive  in  their  nature,  the  small  particles  tend  to  attach  themselves 
to  solid  bodies  with  which  they  come  in  contact.  For  example,  the 
continued  application  of  a  1  per  cent  dilution  of  oil  to  a  branch  for  ten 
minutes  might  result  in  leaving  as  much  oil  on  the  exposed  surface  as  a 
dilution  of  10  per  cent  applied  for  one  minute. 

The  manner  of  application  further  implies  the  force  and  method  used. 
It  is  clear  that  a  spray  thrown  against  the  plant  with  considerable  force 
will  penetrate  more  than  one  which  strikes  lightly.  Mist  sprays  are  for 
this  reason  theoretically  best  for  distillate  work,  but  the  nature  of  the 
foliage  may  modify  this  in  practice. 

With  water-dilution  of  oils,  it  is  impossible  to  get  an  even  distribution 
of  the  oil  over  the  surface,  as  the  water  collects  in  drops,  and  the  contained 
oil  is  deposited  in  spots.  Thus  it  may  happen  that  an  amount  of  oil 
too  small  to  penetrate  if  spread  evenly  over  the  surface  will  do  so  when 
concentrated  on  small  spots. 


SPRAYING    WITH    DISTILLATES.  19 

In  this  connection,  some  experimenting  was  done  with  a  method  of 
applying  the  oil  free  from  water  by  means  of  an  air  blast.  Here  the 
diluting  material  was  air;  and  consequently  a  particle  of  oil  which 
landed  on  any  part  of  the  plant,  did  not  change  its  position  unless  an 
excess  was  used,  when  running  together  took  place.  In  this  way,  the 
maximum  of  oil  can  be  applied  to  a  given  leaf  surface  without  pene- 
tration. 

Influence  of  Weather  Conditions. — The  humidity  of  the  air  largely 
determines  the  extent  to  which  the  stomata,  or  breathing  pores,  are  open, 
and  thus  may  influence  the  penetration  of  oils.  In  general,  the  stomata 
are  more  open  in  moist  weather  than  in  dry.  They  are,  however, 
largely  closed  in  very  dry  air,  but  here  the  extreme  dryness  of  the  leaf 
surface  and  of  the  pore  openings  lend  themselves  to  the  adhesion  and 
inflow  of  the  oils;  so  a  dry  day  may  not  be  as  good  a  time  to  spray  with 
distillates  as  one  moderately  moist. 

Temperature  seems  to  affect  penetration,  at  least  it  has  a  very  marked 
effect  on  the  final  results.  Theoretically,  with  higher  temperatures  the 
oils  are  thinner  and  hence  are  better  adapted  to  capillary  flow.  Another 
potent  factor  in  this  connection  is  that  the  high  temperature  in  this 
climate  is  usually  accompanied  with  low  atmospheric  humidity,  and  so 
adds  to  the  effect  of  the  latter. 

NATURE    OF   INJURY    PRODUCED    BY    OILS. 

There  are,  doubtless,  two  kinds  of  injury  produced  by  oils,  which  we 
may  denominate  chemical  and  physical. 

Physical  Injuries. — The  physical  injury  from  oil  is  due  to  insulation 
or  sealing-over  of  parts  of  the  plant,  preventing  the  access  of  air  to  the 
inclosed  parts.  Insulation  is  also  of  two  kinds,  external  and  internal. 
External  insulation  consists  in  coating  the  outer  surface  of  the  leaf, 
stem,  or  fruit,  as  the  case  may  be,  with  an  air-  and  water-tight  covering. 
If  this  covering  is  of  a  volatile  nature  it  will  pass  away  before  any  harm 
results;  but  if  it  remains  for  a  considerable  time,  much  of  the  char- 
acteristic injury  resulting  from  the  use  of  the  distillate  can  be  obtained 
with  substances  of  a  different  nature. 

The  effect  of  external  insulation  would  necessarily  be  of  two  kinds: 
first,  the  prevention  of  the  loss  of  water;  and  second,  the  exclusion  of  the 
air,  the  oxygen  and  carbon  dioxid  of  which  are  essential  to  plant  life. 

The  normal  loss  of  water,  or  transpiration  of  a  plant  is  very  great,  and 
if  interrupted  there  must  result  some  disorder  in  the  parts  affected. 
The  following  simple  experiments  serve  to  illustrate  the  point  in 
question: 

A  set  of  leaves  was  taken  from  a  growing  plant  and  part  of  them 
coated  with   vaseline;  some  on  the  upper  surface  only,  some  on  the 


20  UNIVERSITY    OF    CALIFORNIA— EXPERIMENT    STATION. 

lower  surface,  and  the  others  on  both  surfaces;  all  being  put  in  a  cool 
place  along  with  the  check  or  untreated  leaves.  Observations  made  from 
time  to  time  showed  considerable  difference  in  behavior.  The  check 
leaves  soon  dried  up,  and  were  followed  somewhat  later  by  those  greased 
on  the  upper  surface  only;  while  those  treated  on  the  under  and  on  both 
surfaces  remained  unchanged  for  a  long  time;  those  coated  on  both 
sides  lasting  the  longest.  Vaseline  has  been  used  in  several  external 
experiments,  but  has  one  objection,  viz. :  When  it  is  heated  up  to  80°  F.,  or 
thereabouts,  it  is  more  or  less  liquid  and  will  penetrate  as  other  oils  do. 
It  is,  however,  a  neutral  substance  and  can  not,  except  when  very  old, 
exert  any  chemical  effect. 

In  order  to  determine  the  amount  of  water  given  off  by  living  leaves 
treated  with  vaseline  in  the  above-mentioned  ways,  they  may  be  inclosed 
in  glass  tubes  without  severing  them  from  the  plant,  and  the  amount  of 
condensation  of  water  noted.  A  record  of  one  such  experiment  shows 
the  following  results:  Four  orange  leaves,  each  having  an  area  of  about 
20  sq.  cm.  on  each  side  of  the  leaf,  were  inclosed  in  test-tubes,  two  checks 
and  two  treated — one  coated  on  the  upper  surface  and  one  on  the  lower 
surface.  An  examination  one  week  later  showed  an  abundance  of  con- 
densation water  in  the  check  tubes  and  also  in  the  one  containing  the 
leaf  treated  on  the  upper  surface;  but  that  containing  the  leaf  treated 
on  the  lower  surface  showed  only  a  very  slight  condensation  on  the  sur- 
face of  the  tube.  Twenty  days  from  the  beginning  of  the  experiment 
the  tubes  were  removed  and  the  condensation  water  measured: 

First  check 0.9  cc. 

Second  check,  dried  up  since  former  observation. 

Treated  upper  surface _._ 0.5  cc. 

Treated  lower  surface  (fallen  from  petiole),  water  not  a  measurable 
quantity. 

Results  similar  to  these  were  obtained  in  other  experiments,  and  show 
in  a  very  striking  manner  the  possible  effect  of  distillates  on  the  trans- 
piration of  plants. 

Insulation  experiments  were  tried  with  other  substances,  such  as 
paraffin,  plaster-of-paris,  etc.,  and  the  results  agree  with  those  cited 
above. 

The  other  possible  effect  of  external  insulation,  namely,  exclusion  of 
the  air  from  affected  parts,  may  be  demonstrated  to  some  extent  by 
covering  ripe  fruit  with  paraffin.  Some  oranges  treated  in  this  way  and 
kept  in  a  cool  place  along  with  the  checks,  showed,  after  three  weeks,  a 
marked  souring  of  the  juice.  This  particular  sample  at  this  time 
showed  no  decay  of  the  rind.  Two  weeks  later  the  wax  on  the  remain- 
ing sample  was  much  inflated  with  gas  bubbles  and  the  rind  showed 
some  fungous  decay.  The  checks  meanwhile  kept  perfectly.  The  well- 
known  observations  on  the  behavior  of  plants  placed  in  a    nitrogen 


SPRAYING   WITH   DISTILLATES.  21 

atmosphere  may  be  cited  in  this  connection.  Strasburger,  in  his  text- 
book of  Botany,  describes  the  effects  produced  as  follows:  "By  placing 
them,  for  example,  under  a  jar  containing  either  pure  nitrogen  or 
hydrogen,  or  in  one  from  which  the  air  has  been  exhausted,  plants  pre- 
viously growing  vigorously  cease  their  growth;  the  streaming  motion  of 
protoplasm  in  the  cells  is  suspended.  Motile  organs  of  the  plant  become 
stiff  and  rigid  and  sink  into  a  death-like  condition";  and  further,  "In 
every  condition  of  rigor,  internal  chemical  changes  take  place,  which, 
by  a  prolonged  exclusion  of  oxygen,  lead  to  the  destruction  and  disor- 
ganization of  the  living  substance." 

The  effect  of  oils  in  internal  insulation  is  much  the  same  as  in  the 
external,  but  here  individual  cells  are  involved  and  consequently  another 
source  of  injury  may  exist,  namely,  that  of  insulation  of  the  cells 
from  one  another,  which  would  lead  to  still  further  complications. 

Internal  insulation  is  a  more  serious  problem  in  practical  spraying 
than  the  external,  for  the  reason  that  it  is  most  liable  to  occur.  Less  oil 
is  required  to  effect  a  complete  covering,  because  it  is  protected  from 
evaporation,  and  hence  remains  for  a  long  time. 

Two  distinct  kinds  of  injury  result  from  insulation,  and  probably 
correspond  to  the  two  effects  obtained  by  exclusion  of  air,  assisted  by 
prevention  of  transpiration.  These  injuries  may  be  classed  as  rapid 
and  chronic. 

The  rapid  injuries,  when  a  neutral  substance  is  used,  depend  largely 
on  the  temperature,  and  consist,  in  the  citrus  plants,  of  a  rapid  falling 
of  the  leaves  affected,  without  any  apparent  change  in  them.  In  warm 
weather,  70°  to  90°  F.,  this  falling  takes  place  in  leaves  treated  with 
vaseline  or  paraffin,  in  from  two  to  three  days;  but  leaves  treated  in 
the  same  way  may  require  two  or  three  weeks  to  be  affected  in  cool 
weather,  say  at  50°  to  60°  F.  This  difference  may  be  due  to  the  lack  of 
transpiration,  which  allows  the  leaf  to  become  hotter  than  it  would  at 
the  same  temperature  in  the  normal  state,  and  thus  produces  a  sort  of 
heat-killing.  It  is  possible  that  the  dropping  may  be  brought  about  in 
another  way.  If  the  air  is  excluded  from  the  greater  part  of  the  leaf, 
the  heat  which  would  normally  bring  about  healthy  cell  action  might 
cause  the  production  of  toxic  substances;  these  would  be  communicated 
to  the  weak  cork-forming  cells  at  the  base  of  the  stalk  and  cause  their 
death  and  desiccation  and  a  consequent  formation  of  the  cork  layer, 
resulting  in  the  falling  of  the  leaf. 

The  chronic  effect  is  very  different,  being  much  slower.  It  also  brings 
about  a  loss  of  color,  a  yellowing  in  the  affected  parts  and  consequent 
lack  of  growth  or  other  processes,  which  may  result  in  the  fall  of 
the  leaf  some  weeks  or  months  after  the  application.  In  the  orange, 
the  chronic  effect  of  stem-coating  often  brings  about  violent  exudation 
of  gum,  resembling  the  gum  disease.     This  effect  is  also  seen  occasionally 


22  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

in  ordinary  distillate  spraying,  and  is  most  evident  when  the  spraying 
has  been  done  in  warm  weather. 

The  yellowing  is  most  noticeable  in  green  orange  fruit  or  leaves  which 
have  been  treated  with  vaseline.  In  from  three  to  four  days  the  color 
of  the  fruit  begins  to  lighten,  and  it  may,  in  the  course  of  a  month, 
assume  the  brightness  of  the  normal  ripe  fruit. 

Chemical  Injury  by  Oils. — The  injury  which  is  due  to  insulation  could 
just  as  well  be  produced  by  any  substance  which  would  exclude  air  and 
retain  water;  but  most  oils  have  a  direct  chemical  effect,  induced  by 
their  vapor.  If  a  growing  plant  is  inserted  into  a  bottle  containing  a 
small  amount  of  oil  showing  this  chemical  effect,  and  the  bottle  is 
corked  or  sealed  for  several  hours  in  such  a  way  as  not  to  break  or  harm 
the  branch,  the  effect  of  the  vapor  may  be  noted.  In  this  connection 
three  tests  made  with  orange  foliage  are  worthy  of  note.  In  the  first, 
a  saturated  gasoline  atmosphere  was  used.  Time  of  application,  half 
an  hour.  Twenty-four  hours  later  the  tips  of  the  leaves  nearest  the 
liquid  gasoline  in  the  bottom  of  the  bottle  were  wilted,  and  later  dried 
out  quite  white,  otherwise  the  leaves  appeared  normal;  but  in  about 
sixty  hours  a  general  bleaching  was  noted.  (This  was  a  whitening  and 
differed  from  the  yellowing  previously  referred  to.)  This  bleaching  was 
followed  by  the  falling  of  all  the  treated  leaves,  which  was  complete  in 
one  hundred  and  twenty  hours  from  the  beginning  of  the  experiment. 

In  the  second  experiment,  Franklin  Refining  Company's  28°  B.  distil- 
late was  used.  The  leaves  were  exposed  three  and  four  hours  respec- 
tively, with  similar  results.  A  decided  bleaching  of  the  treated  foliage 
was  noted  in  seventy-two  hours,  accompanied  by  the  falling  of  the 
tenderest  leaves  of  the  new  growth,  namely,  those  just  expanded  from 
the  bud;  later,  most  of  the  older  leaves  fell. 

In  the  third  experiment,  Southern  Refining  Company's  28°  B.  (short- 
cut) distillate  was  used.  The  application  lasted  five  hours,  and  resulted 
in  a  decided  bleaching  of  the  lower  surface  of  the  leaves,  which  were  also 
somewhat  curled  and  distorted;  but  no  falling  took  place. 

The  results  of  these  experiments  are  sufficient  to  show  that  the 
chemical  effect  of  oils  is  entirely  different  from  that  of  insulation, 
although  it  brings  about  the  same  ultimate  result,  namely,  the  falling 
of  the  leaves. 

The  nature  of  this  chemical  effect  is  not  so  easy  to  explain  as  that  of 
insulation,  but  it  is  safe  to  say  that  it  is  always  present  in  spray  distil- 
lates, although  some  show  it  less  than  others.  This  is  probably  the 
most  important  insecticidal  feature  of  oils,  and  it  affords  the  best 
method  of  explaining  the  very  marked  insecticidal  effect  of  some  of 
them.  For  instance,  in  hopper-dozer  work  it  is  sufficient  that  the  insect 
touch  the  oiled  surface  with  any  part  of  its  body  in  order  to  bring  about 


SPRAYING   WITH    DISTILLATES.  23 

death  in  a  few  hours.  Insects  are  probably  more  subject  to  the  chemi- 
cal effect  of  oils  than  are  plants,  and  may  even  respond  in  a  different 
way. 

With  those  oils  which  contain  gasoline,  the  effect  of  their  vapor  on 
vegetable  tissue  is  rather  slow  in  developing,  and  partakes  of  a  chronic 
nature,  from  which  the  affected  parts  recover  slowly. 

RESISTANCE   OF   THE    PLANT    TO   INJURY    BY    OILS. 

All  plants  are  not  alike  in  their  response  to  distillates  or  oils,  and 
the  citrus  plants  were  found  to  be  among  the  most  hardy  in  this  respect. 
There  is  also  considerable  difference  in  the  resistance  in  varieties  of  the 
same  species.  For  instance,  distillate  spraying  has  long  been  considered 
a  success  on  lemons,  while  it  has  not  succeeded  on  oranges  until  the 
advent  of  the  mechanical  mixing  process,  and  is  even  yet  of  doubtful 
utility.  Grape-fruit  is  even  more  sensitive  than  the  orange.  All  decid- 
uous trees  experimented  with  have  proved  very  susceptible  to  injury  by 
the  distillates  other  than  kerosene. 

The  nature  of  the  injury  to  the  orange  and  apricot  foliage  also  diners 
somewhat;  with  apricot,  the  spots  showing  penetration  were  much  more 
localized  and  the  oil  in  each  spot  more  concentrated,  and  consequently 
a  withering  of  parts  of  leaves  occurred,  due  to  the  rapid  killing  of  the 
cells  which  were  entirely  surrounded  by  the  oil.  This  greater  localiza- 
tion of  oil  on  the  apricot  leaf  is  due  to  the  less  penetrable  vascular  bun- 
dles coming  in  close  contact  with  the  epidermis  (see  Figs.  2  and  3,  pp. 
12-13),  thus  making  dams  which  prevent  the  greater  diffusion  of  pene- 
trated oil,  as  compared  with  the  orange  leaf,  where  the  bundles  are 
buried  in  the  green  pulp  between  the  skins.  Corresponding  doses  of 
distillate  are  much  more  injurious  to  the  apricot  leaf,  as  a  whole,  than 
to  orange  foliage,  notwithstanding  the  above-mentioned  fact  in  reference 
to  the  localization  trouble.  In  addition  to  the  localized  injuries,  the 
leaves  of  the  apricot  treated  with  distillate  became  yellow,  and  fell,  the 
petiole  breaking  from  the  stem  as  in  the  natural  falling  of  an  old  leaf. 
The  orange  leaf,  on  the  other  hand,  may  not  show  any  signs  of  injury, 
but  will  break  off  at  the  juncture  of  petiole  and  blade  in  from  three  to 
ten  days  from  the  time  of  treatment,  falling  taking  place  most  and 
soonest  in  hot  weather. 

But  injury  is  not  confined  to  the  leaves  which  drop.  All  treated 
leaves  are  more  or  less  injured  and  recover  very  slowly  from  the  effects 
of  the  heavy,  slow-drying  oils.  A  loss  of  color  may  be  noted  in  from 
ten  to  fifteen  days,  and  the  leaf  may  never  regain  its  former  green 
appearance.  The  same  dropping  and  yellowing  effect  that  is  seen  in  the 
leaves  takes  place  with  the  fruit  also.  In  fact,  the  young  fruit  is  much 
more  sensitive  than  are  the  leaves  to  the  " dropping''  effect  of  distil- 
lates.    The  yellowing  effect  is  most  noticeable  in  the  class  of  plants  to 


24  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

which  the  prune  and  apple  belong.  The  color  of  the  matured  leaf  may- 
be completely  changed  in  three  or  four  days  by  the  use  of  very  weak 
dilutions  of  the  28°  distillates,  and  from  what  has  been  observed  in 
these  experiments,  most  deciduous  plants,  when  in  leaf,  should  not  be 
sprayed  with  the  heavy  distillates. 

Variegated  Leaves. — Chronic  effects  are  induced  by  diseased  and 
depleted  conditions  of  the  tree  in  general.  The  trouble  known  as 
variegated  leaf  was  observed  to  render  the  trees  affected  by  it  quite 
sensitive  to  distillates.  Also  the  yellow  or  dormant  condition  of  the 
foliage  and  tree,  due  to  lack  of  nitrogenous  fertilizer,  greatly  increased 
the  liability  of  injury  from  an  oily  spray  material.  The  old  leaves  in 
a  normal  condition  are  very  sensitive,  being  drier  than  the  new  leaves 
and  in  a  slow  state  of  vegetative  activity.  Such  leaves  will  usually 
fall  from  any  tree  sprayed  with  distillates,  a  fact  which  is  sometimes 
cited  by  sprayers  as  an  advantage  of  the  process;  namely,  the  removal 
of  old  and  useless  foliage.  But  it  must  be  remembered  in  this  connec- 
tion, that  the  cause  which  effects  the  falling  of  some  leaves  on  a  tree 
also  operates  in  the  same  direction  on  every  leaf,  with  a  resulting 
depressing  effect. 

Effect  of  Temperature. — Another  and  very  important  feature  in  the 
resistance  of  plants  to  distillate  effects  is  the  temperature  of  the  air. 
This  was  dealt  with  to  some  extent  under  the  head  of  penetration,  on 
page  11. 

There  are  two  possible  ways  in  which  a  temperature  of  about  80°  F. 
might  affect  leaves  treated  with  distillates.  The  first  relates  to  the 
insulation  caused  by  the  oils  and  the  consequent  checking  of  transpira- 
tion, or  the  giving-off  of  water  by  the  plant.  It  may  be  roughly 
likened  to  a  man  hard  at  work  and  yet  unable  to  perspire.  He  would 
soon  become  overheated  and  prostrated.  In  the  same  way  the  leaves  of 
a  plant  might  become  overheated  if  the  transpiration-current  were  cut 
off,  except  that  in  the  case  of  the  plant  the  heat  must  be  supplied  from 
the  outside. 

It  has  been  demonstrated  by  experiment  that  insulation  will  cause 
the  falling  of  a  leaf  in  two  or  three  days,  if  the  leaf  is  in  the  direct  sun- 
light or  in  a  warm  location;  but  leaves  treated  in  the  same  way  and 
kept  in  a  cool  place  may  remain  on  the  plant  for  several  weeks  without 
change. 

The  temperature  may  also  affect  results  by  increasing  the  amount  and 
rate  of  oil-vaporization,  for  if  the  vapor  of  an  oil  has  any  effect  it  will 
increase  with  the  amount  present,  and  perhaps  this  factor  is  as 
important  as  the  heat  itself. 

Aside  from  the  matter  of  variety,  the  condition  of  the  plant  largely 
controls  its  behavior  toward  distillates.     Plants  in  vigorous  growth  are 


SPRAYING    WITH    DISTILLATES.  25 

much  more  resistant  than  those  in  a  dormant  condition.  This  was 
constantly  noticed  in  experimenting  with  the  effect  of  oils.  For  these 
reasons  distillates  are  most  satisfactory  where  applied  in  the  cool 
weather  of  the  fall  and  winter. 

PRACTICAL  SUGGESTIONS. 

The  question  of  how  far  the  use  of  an  oil  spray  can  be  profitably  carried 
with  citrus  trees  depends  on  its  effectiveness  when  compared  with  other 
methods  of  disinfection.  As  the  spray  kills  by  contact  and  soon 
evaporates,  the  effectiveness  of  any  one  operation  extends  over  but  a 
short  period.  Practically  any  insect  not  killed  at  once,  escapes,  although 
there  is  a  slight  tendency  to  chronic  injury  and  slow  death,  just  as  in 
plants. 

Repeated  experiments  and  observations  of  distillate  spraying-work 
done  in  citrus  orchards  in  southern  California  have  shown  that  large 
numbers  of  insects  and  mites  escape  the  most  careful  spraying,  and 
naturally  this  number  increases  with  the  dilution  of  the  wash.  In  fact, 
it  has  been  found  necessary,  in  order  to  avoid  serious  injury  to  the  trees, 
to  dilute  the  sprays  so  much  that  the  hardier  and  more  protected  stages 
of  the  various  scale  insects  survive  in  sufficiently  large  numbers  to 
quickly  and  completely  reinfest  the  tree,  if  the  treatment  stops  with 
one  application. 

In  the  case  of  the  black  scale  the  evidence  in  this  particular  is  most 
complete.  The  first  spraying  with  a  28°  B.  distillate  of  from  2  to  3  per 
cent  dilution  results  in  the  death  of  most  of  the  scales  in  the  active 
growing  stages,  often  killing  scales  nearly  full  grown.  The  results  of 
such  spraying  can  be  determined  by  inspection  in  about  a  week  after 
application.  (The  few  that  die  later  from  the  effects  of  the  treatment 
do  not  affect  materially  the  conclusions  reached.)  The  dead  scales  will 
then  be  shriveled  and  many  will  have  fallen  from  the  tree.  The  majority 
of  those  living  will  be  found  to  be  old  scales  covering  numerous  eggs, 
which  have  also  remained  unaffected.  In  some  cases  the  old  scales  may 
be  somewhat  loosened,  thus  aiding  the  emergence  of  the  young  from 
beneath  the  shell. 

Quite  often,  an  extensive  appearance  of  young  scales  is  noticeable  in 
from  two  to  three  weeks  after  spraying.  These  and  other  young,  which 
emerge  from  time  to  time,  may  reinfest  the  tree,  making  its  condition 
as  serious  as  ever  in  from  six  to  seven  months  after  the  first  spraying. 
Owing  to  this  fact  it  is  necessary  to  repeat  the  spraying  two  or  three 
times,  allowing  some  months  between  applications.  The  operations 
should  be  at  least  two  months  apart,  the  object  being  to  reach  as  many 
as  possible  of  the  insects  while  still  in  their  more  sensitive  condition, 
and  to  give  the  tree  time  to  recover  from  the  last  spraying.  The  first 
spraying  may  so  reduce  the  number  of  scales  on  a  tree  that  all  smutting 


26  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT    STATION. 

and  injury  from  this  source  ceases  for  the  time  being,  and  if  the  oper- 
ations are  repeated  properly  will  often  result  in  a  fairly  clean  tree. 

The  red  spider  offers  a  somewhat  different  problem.  Here  the  eggs 
are  exposed  to  the  action  of  the  spray,  and  can  be  killed  with  from 
1  to  2  per  cent  dilution  of  a  28°  B.  distillate;  but  in  practical  spraying 
many  mites  escape,  presumably  those  which  have  not  been  touched  by 
the  spray,  and  the  time  which  should  be  allowed  to  lapse  between 
applications  of  the  spray  will  often  be  sufficient  for  a  complete  rein- 
festation  of  the  tree.  Thus  the  control  of  the  mites  may  be  even  more 
doubtful  than  that  of  the  black  scale. 

Injury  to  Plant. — None  of  these  sprayings  can  be  done  without  more 
or  less  injury  to  the  tree  and  fruit,  but  there  are  times  of  the  year  and 
manners  of  application  which  make  it  possible  to  spray  with  distillates 
without  this  injury  being  very  serious. 

The  injury  caused  by  distillates  to  the  plant  may  be  briefly  summa- 
rized as,  first,  the  rapid  falling  of  leaves  and  young  fruit,  which  takes 
place  in  from  three  to  ten  days  after  the  application;  second,  the  yellow- 
ing and  slower  falling  of  these  parts,  resulting  from  the  prolonged  or 
chronic  effects  of  the  distillate.  The  rapid  falling  takes  place  most  and 
soonest  in  hot  weather,  and  perhaps  the  chronic  effects  are  also  most 
felt  at  this  time.  The  amount  of  injury  resulting  from  spraying  is  also 
much  less  on  healthy  trees;  that  is,  trees  in  good  growing  condition  and 
not  suffering  from  yellow-leaf,  lack  of  water,  or  scale.  As  the  amount 
of  water  in  the  plant  can  be  remarkably  increased  by  the  watering  of 
the  soil,  it  would  seem  a  good  practice  in  hot  weather  to  spray  as  soon 
after  irrigation  as  possible,  for  at  such  times  the  plant  would  contain 
most  water,  and  would  therefore  be  less  penetrable  to  distillates.  But 
in  general,  the  results  from  spring  and  summer  spraying  of  orange  trees 
have  been  such  as  to  indicate  that  the  plant  will  always  suffer  enough 
during  these  seasons  to  make  treatment  with  distillates  inadvisable. 
Not  that  the  plant  in  general  will  be  most  damaged  at  such  times,  but 
that  the  young  fruit  is  then  most  susceptible,  both  to  spotting  and 
dropping. 

Spotting  and  Dropping  of  Fruit. — There  is  no  doubt  that  dropping  of 
young  fruit  is  greatly  increased  by  distillate  spraying,  and  may  even 
bring  about  falling  of  fruit  in  sizes  which  are  normally  beyond  such  a 
possibility.  The  brown  spot  or  stain  which  appears  on  ripe  fruit  that 
has  been  sprayed  during  the  season,  is  also  most  liable  to  be  formed 
when  the  fruit  is  young;  that  is,  from  half-grown  to  within  a  few  weeks 
of  coloring.  These  spots  may  be  noticed  in  the  green  fruit  as  somewhat 
duller  and  darker  blotches  just  under  the  skin  of  the  rind.  They  do 
not  change  much  as  the  fruit  grows  older,  and  when  coloring  takes 
place  they  remain  brown.  Such  spots  do  not  injure  the  orange  in  any 
way  except  appearance. 


SPRAYING    WITH    DISTILLATES.  27 

It  is  hardly  possible  to  spray  with  a  heavy  distillate  (that  is,  28°  B. 
to  26°  B.)  without  injuring  young  fruit  by  spotting  or  dropping.  Then 
if  it  is  intended  to  spray  with  distillates,  it  is  not  advisable  to  do  so  in 
the  spring  or  early  summer,  but  the  best  results  will  be  obtained  from 
October  until  January.  In  October  the  orange  rind  has  developed  and 
is  much  more  difficult  to  spot  than  earlier  in  the  season;  also  the 
weather  is  cooler,  and  the  general  effects  of  distillates  on  the  plant  are 
much  less  severe.  Leaf  falling  will  not  be  so  noticeable,  and  yellowing 
of  the  leaves  will  not  be  so  marked.  The  fruit  is  also  naturally  begin- 
ning to  color  at  that  time,  so  any  artificial  increase  in  this  tendency  will 
not  be  a  detriment. 

But  it  may  be  argued  that  the  early  broods  of  the  black  scale  will  be 
too  large  to  be  killed  late  in  the  fall.  This  would  be  a  greater  difficulty 
if  it  were  not  for  the  fact  that  most  of  the  early  brood  die  during  the 
summer.  It  is  either  parasitized  or  dies  from  heat,  and  also  from 
drought,  which  may  put  the  tree  in  such  a  condition  as  to  kill  the 
scale.  In  this  way  the  earlier  broods  of  scale  are  often  nearly  elimi- 
nated from  the  problem  of  disinfection. 

Two  Sprayings  Annually. — Now  if  the  problem  of  fruit  injury  did  not 
enter  into  consideration,  the  spraying  in  October  or  November  should  be 
followed  by  a  second  application  at  the  time  the  scales,  which  hatched 
from  the  eggs  not  injured  by  the  first  application,  had  arrived  in  part  at 
the  maximum  killable  size.  This  would  naturally  insure  the  greatest 
efficiency  to  the  second  operation.  But  the  scales  might  not  reach  this 
condition  until  well  into  the  growing  season  of  the  following  spring, 
when  spraying  with  distillates  is  inadvisable.  The  second  application 
should  therefore  be  made  in  January  and  February,  or  just  before  the 
flower  spurs  start.  The  scales  which  escape  that  operation  should  be 
left  again  until  October  or  November,  when  the  routine  should  be 
repeated. 

This  provides  for  two  sprayings  a  year,  and  yet  may  not  be  sufficient 
to  insure  perfectly  clean  trees;  but  such  can  not  be  obtained  by  spraying 
unless  the  treatment  is  planned  wholly  with  regard  to  the  scales,  and 
not  considering  the  most  desirable  time  with  regard  to  the  plant.  Three 
or  four  applications  will  be  found  necessary  to  clean  badly  infested  trees 
and  bring  the  efficiency  of  this  method  of  disinfection  up  with  that  of 
proper  fumigation. 

The  two  sprayings  a  year,  timed  as  before  stated,  are  not  only  all 
that  is  desirable  from  the  point  of  plant  resistance,  but  also  reaches  the 
limit  of  the  economic  advantage  which  spraying  has  over  fumigation; 
for  experience  has  shown  that  spraying  will  not  be  cheaper  than  fumiga- 
tion if  three  or  four  applications  are  required.  Further,  if  a  schedule  of 
fall  and  early  spring  sprayings  is  adopted,  it  will  also  result  in  the  best 
control  of  the  red  spider  which  can  be  obtained  with  two  sprayings. 


28  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 

Where  spraying  is  done  early  in  the  season,  or  during  the  spring  and 
summer,  the  spider  may  be  numerous  again  during  the  fall  and  winter, 
for  distillates  really  leave  a  large  number  of  mites  alive,  which  by  means 
of  their  rapid  breeding  may  become  abundant  again  in  a  few  months. 

If  the  spider  is  abundant  in  the  late  spring,  early  summer,  or  in  the  fall, 
sulfur  spraying  is  advisable  before  spraying  with  distillates.  The  same 
machinery  can  be  used,  but  the  material  will  cost  more.  It  is  advised 
by  some  to  use  a  weak  distillate  spray  in  such  cases,  but  it  must  be 
remembered  that  the  labor  factor  is  the  same  as  for  a  full  straight  dose, 
and  it  is  not  nearly  so  effective;  besides,  it  is  not  possible  to  so  reduce 
the  strength  of  the  distillate  (28°  B.  or  thereabouts)  that  it  will  not 
affect  the  plant,  and  especially  the  fruit. 

PREVENTION    OF    INJURY    FROM    SPRAYING. 

The  question  of  injury  to  the  plant  is  one  of  such  serious  consequence 
that  any  change  in  the  manner  or  time  of  application  which  will  reduce 
the  same,  is  of  consequence  to  those  who  wish  to  spray  with  distillates. 
Next  in  importance  to  the  time  would  come  the  system  used  in  apply- 
ing the  wash.  The  method  which  naturally  suggests  itself  is  to  wet 
every  part  of  the  tree  as  thoroughly  as  possible,  so  that  no  insect 
may  escape.  In  order  to  do  this  great  care  must  especially  be  taken  to 
wet  the  under  side  of  the  leaves.  But  the  experiments  detailed  above 
have  shown  that  the  under  side  of  a  leaf  is  most  sensitive  to  distillate 
injury,  while  the  upper  side  is  comparatively  resistant.  It  is  obvious 
that  the  spray  hurled  up  under  the  leaves  is  proportionally  much  more 
injurious  to  the  tree  than  that  applied  from  above. 

Overshot  Sprays.—  The  overshot  method  involves  spraying  as  nearly 
straight  down  as  possible,  beginning  with  the  top  of  the  tree  and  pro- 
ceeding toward  the  sides  and  bottom.  Ladders  are  necessary  to  apply 
this  method  to  large  trees,  as  the  sprayer  must  see  what  he  is  doing. 
With  this  method  it  is  possible  to  use  about  double  the  per  cent  of  oil 
without  as  much  injury  as  results  from  the  ordinary  strengths  applied 
in  the  common  way. 

The  overshot  method  wets  much  more  than  50  per  cent  of  the  stems, 
but  leaves  most  of  the  leaves  dry  on  the  under  side;  so  if  an  overshot 
spraying  was  done  with  a  4  per  cent  dilution,  and  some  ordinary  spray- 
ing done  with  2  per  cent,  the  overshot  spraying  might  kill  the  greater 
number  of  scales  and  at  the  same  time  do  less  injury  to  the  tree.  There 
are  two  difficulties  in  the  practical  application  of  the  overshot  method; 
first,  the  spotting  of  the  fruit  is  not  overcome;  and  second,  the  red 
spider,  if  present,  will  be  left  in  large  numbers  on  the  under  side  of  the 
leaves. 

Whatever  may  be  the  chemistry  and  physics  of  the  commoner  form 
of  fruit  spot  caused  by  distillates,  it  is  evident  that  it  is  produced  by 


SPRAYING    WITH    DISTILLATES.  29 

the  presence  of  the  oil  upon  limited  areas  of  the  rind.  These  excessive 
amounts  are  large  drops  of  the  liquid  left  hanging  to  the  rind  of  the 
fruit  after  the  application  has  been  made.  The  spots  will  be  somewhat 
larger  than  the  drops,  owing  to  the  spread  of  the  oil  beneath  the  rind. 
The  oil  in  the  drops  becomes  more  and  more  concentrated  by  the  evapo- 
ration of  water,  and  is  finally  left  in  a  free  state  on  the  surface  of  the 
rind,  from  whence  it  penetrates  the  tissue.  This  form  of  spot  will  be 
present  to  some  extent  on  fruit  sprayed  by  the  overshot  method.  The 
part  of  the  fruit  exposed  directly  to  the  action  of  the  spray  is  wet,  and 
drops  of  the  wash  run  down  the  sides  and  hang  from  the  lower  surface. 
The  general  surface  of  the  fruit  is,  however,  less  injured  by  overshot 
spraying  than  by  the  ordinary  methods. 

Combined  Spraying. — In  view  of  the  spotting  and  the  red  spider  diffi- 
culties which  still  remain  with  the  overshot  method,  it  is  evident  that 
it  will  have  to  be  supplemented  if  we  would  take  full  advantage  of  the 
greater  resistance  that  the  upper  surfaces  of  the  leaves  have  to  distillates. 
If  the  overshot  application  is  followed  by  a  slight  undershot  spraying 
with  a  much  weaker  dose,  the  large  drops  of  strong  mixture  left  by  the 
overshot  application  will  be  replaced  by  a  much  weaker  mixture,  but 
still  of  sufficient  strength  to  kill  the  red  spider.  To  make  this  plan 
successful  the  undershot  application  must  be  made  very  soon  after  the 
overshot,  which  would  require  the  use  of  two  machines:  one  to  do  the 
overshot  work  and  one  to  follow  doing  the  undershot.  It  is  possible 
to  modify  the  types  of  machines  now  in  use  so  that  both  overshot  and 
undershot  work  can  be  done  by  the  same  outfit. 

The  existing  spraying  machines  can  be  modified  for  overshot  work  by 
placing  a  smaller  pump  on  the  piston  rod,  designed  to  carry  somewhat 
less  than  one  third  the  liquid  thrown  by  the  large  pump.  This  small 
pump  is  connected  with  the  discharge  of  the  large  pump  and  also  the 
water  tank  by  adjustable  valves.  The  discharge  of  each  pump  is  con- 
nected with  a  separate  pressure  tank  and  thence  to  the  hose — the  large 
pump  supplies  two  lines  of  hose  and  the  small  pump  one.  In  operation, 
part  of  the  mixed  water  and  oil  thrown  by  the  large  pump  is  drawn 
into  the  small  one  and  again  diluted  with  water  from  the  tank,  so  that 
while  the  large  pump  might  be  throwing  a  dilution  of  4  per  cent,  the 
small  one  would  deliver  a  1  per  cent  wash,  or  any  other  proportions 
which  might  be  desired.  This  mechanism  overcomes  the  trouble  with 
the  very  fine  valve  adjustment  required  to  introduce  1  per  cent  of  oil 
directly  into  the  water. 

This  attachment  can  be  placed  on  any  form  of  machine.  With  the 
double  suction  patterns  the  oil  is  introduced  into  the  large  pump,  and 
in  the  agitator  machines  an  extra  water  tank  must  be  carried  to  furnish 
the  water   for   the   small   pump.     The   double   suction   machines   are 


30  UNIVERSITY    OF   CALIFORNIA— EXPERIMENT    STATION. 

evidently  best  adapted  for  this  attachment,  because  one  water  tank 
serves  both  pumps. 

In  this  way  two  lines  of  hose  could  be  used  for  the  overshot  work, 
applying  the  spray  at  from  3-J  to  4  per  cent  oil  content,  while  one  line 
would  be  occupied  with  the  undershot  work,  using  a  1  per  cent  wash. 
The  overshot  application  should  be  quite  thorough,  beginning  at  the  top 
of  the  tree  and  extending  down  the  sides,  while  the  undershot  operation 
might  consist  in  rapidly  going  over  the  under  sides  of  the  fruit  to 
remove  the  large  drops.  This  would  result  in  a  slight  wetting  of  the 
under  side  of  the  foliage,  in  most  cases  not  enough  to  result  in  serious 
injury.  Those  who  are  not  provided  with  such  a  machine  may  make 
some  use  of  the  overshot  idea  by  applying  most  of  the  wash  from  above 
and  throwing  as  little  up  under  the  leaves  as  is  possible  for  thorough 
work. 

There  are  also  some  minor  points  in  application  which  should  not  be 
neglected.  For  instance,  an  excessive  amount  should  not  be  applied, 
for  the  oil  accumulates  on  the  leaves,  and  the  effect  of  a  4  per  cent 
wash  may  be  had  with  a  2  per  cent  dilution.  Again,  a  very  dashing, 
heavy  spray  will  penetrate  far  more  than  a  fine  mist,  but  the  nature  of 
the  orange  foliage  seems  to  limit  the  extent  to  which  the  mist  sprays 
can  be  used.  This  is  especially  true  when  the  tree  is  loaded  with  fruit. 
All  the  branches  are  then  bent  down  and  the  leaves  are  held  in  place 
by  the  weight  of  the  fruit.  Under  these  conditions  it  seems  necessary 
to  use  a  somewhat  coarser  spray.  Spraying  outfits  usually  come 
equipped  with  satisfactory  nozzles.  These  are  nearly  all  modifications 
of  the  cyclone  type.  The  favorite  extension  rod  has  two  cyclone  nozzles 
about  a  foot  apart  on  a  cross-arm,  which  is  borne  at  right  angles  to  the 
main  rod.  The  nozzles  are  attached  to  this  rod  by  means  of  an  elbow. 
In  this  way  there  are  no  sharp  corners  or  projections  to  catch  in  the  tree. 
The  nozzles  of  the  Vermorel  type,  having  a  plunger  for  cleaning,  are 
objectionable  on  this  account. 

Oil  to  be  Used. — The  question  of  the  oil  to  be  used  in  spraying  work 
is  quite  important.  In  the  early  history  of  distillate  spraying,  attempts 
were  made  to  use  much  lighter  oils  than  those  in  more  recent  practice. 
At  that  time  the  emulsions  offered  the  only  means  of  handling  the  oils, 
and  it  was  found  very  difficult  to  make  very  stable  emulsions  with  Cali- 
forina  light  kerosenes,  considerable  injury  being  produced  by  the  sepa- 
rated oil.  For  these  reasons  heavier  oils  have  been  used  with  better 
results,  so  far  as  emulsions  are  concerned;  but  apparently  these  heavy 
oils  are  far  worse  than  the  kerosenes  in  their  general  effect  on  the  plant. 

With  Eastern  kerosene  it  was  found  that  25  per  cent  of  oil  was  less 
injurious  than  5  per  cent  of  a  28°  B.  Western  distillate.  The  kerosenes 
are  also  somewhat  less  effective  as  insecticides,  but  not  in  proportion  to 


SPRAYING    WITH    DISTILLATES.  31 

their  neutrality  to  plants.  This  is  due  to  the  fact  that  insects  are  much 
more  quickly  affected  than  vegetable  tissue,  and  with  a  volatile  oil  the 
plant  might  escape  injury  where  animal  life  would  be  destroyed. 

A  sample  of  Western  kerosene  tried  did  not  give  as  good  results  as 
the  Eastern  article,  but  this  was  probably  due  to  its  greater  content  of 
benzine  and  gasoline,  which  substances  are  very  volatile  and  severe  in 
their  action  on  plant  tissue.  But  there  is  no  reason  why  kerosene, 
sufficiently  pure  to  be  used  in  spraying,  could  not  be  prepared  by  the 
refining  companies  at  a  reasonable  cost.  Such  oils  could  be  used  if 
they  could  be  had  for  from  8  to  10  cents  per  gallon.  The  cost  of  the 
heavier  distillates  ranges  from  5  to  7  cents  per  gallon,  and  the  low  per 
cents  used  make  the  expense  of  the  material  very  small;  but  it  is  a 
question  whether  the  orchardist  prefers  the  cheapest,  regardless  of  con- 
sequences. Kerosenes  are  now  quite  extensively  used  in  Eastern  prac- 
tice, and  the  per  cents  run  rather  high,  25  per  cent  of  oil  content  being 
more  common  there  than  2  per  cent  with  Western  distillates. 

The  orange  tree  will  withstand  from  8  to  10  per  cent  of  kerosene,  used 
in  ordinary  spraying,  and  15  per  cent  in  overshot  work.  These  strengths 
are  sufficient  to  kill  young  scale  and  the  red  spider.  Kerosene  has  the 
same  limitations  as  the  heavier  oils,  and  several  applications  are 
required  to  clean  a  tree  of  most  insects.  It  can  also  be  applied  to  other 
than  citrus  plants  with  greater  safety  than  the  heavier  distillates.  In 
fact,  kerosene  oil  has  many  points  to  commend  it  to  orchardists  who 
wish  this  kind  of  an  insecticide,  but  in  all  cases  an  article  reasonably 
free  from  impurities  should  be  insisted  upon. 


REPORTS  AND  BULLETINS  AVAILABLE  FOR  DISTRIBUTION. 


REPORTS. 


Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regarding 
the  Vintages  of  1894-95. 

1897.  Resistant  Vines,  their  Selection,  Adaptation,  and  Grafting.    Appendix  to  Viti- 

cultural Report  for  1896. 

1898.  Partial  Report  of  Work  of  Agricultural  Experiment  Station  for  the  years  1895-96 

and  1896-97. 
1900.    Report  of  the  Agricultural  Experiment  Station  for  the  year  1897-98. 
1902.    Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

BULLETINS. 

No.  115.  Remedies  for  Insect  and  Fungi.    (Revised.) 

121.  The  Conservation  of  Soil  Moisture  and  Economy  in  the  Use  of  Irrigation  Water. 

125.  Australian  Saltbush. 

^127.  Bench-Grafting  Resistant  Vines. 

128.  Nature,  Value,  and  Utilization  of  Alkali  Lands. 

129.  Report  of  the  Condition  of  Olive  Culture  in  California. 
*  131.  The  Phylloxera  of  the  Vine. 

132.  Feeding  of  Farm  Animals. 

133.  Tolerance  of  Alkali  by  Various  Cultures. 

v  134.  Report  of  Condition  of  Vineyards  in  Portions  of  Santa  Clara  Valley. 

135.  The  Potato-Worm  in  California. 

s  136.  Erinose  of  the  Vine. 

*•»  137.  Pickling  Ripe  and  Green  Olives. 

138.  Citrus  Fruit  Culture. 

139.  Orange  and  Lemon  Rot. 

140.  Lands  of  the  Colorado  Delta  in  Salton  Basin,  and  Supplement. 

141.  Deciduous  Fruits  at  Paso  Robles. 

142.  Grasshoppers  in  California. 

143.  California  Peach-Tree  Borer. 

144.  The  Peach-Worm. 

145.  The  Red  Spider  of  Citrus  Trees. 

146.  New  Methods  of  Grafting  and  Budding  Vines. 

147.  Culture  Work  of  the  Substations. 

148.  Resistant  Vines  and  their  Hybrids. 

149.  California  Sugar  Industry. 

150.  The  Value  of  Oak  Leaves  for  Forage. 

151.  Arsenical  Insecticides. 

152.  Fumigation  Dosage. 

Copies  may  be  had  by  application  to  the  Director  of  the  Experiment 
Station,  Berkeley,  California. 


